1. Field of the Invention
The present invention relates to a transfer material and process for offset printing of a heat transferable material having a transfer blocking overcoat.
2. Description of the Prior Art
Textiles such as shirts (e.g., tee shirts) having a variety of designs thereon have become very popular in recent years. Many shirts are sold with pre-printed designs to suit the tastes of consumers. In addition, many customized tee shirt stores are now in the business of permitting customers to select designs or decals of their choice. Processes have also been proposed which permit customers to create their own designs on transfer sheets for application to tee shirts by use of a conventional hand iron, such as described in U.S. Pat. No. 4,244,358 issued Sep. 23, 1980. Furthermore, U.S. Pat. No. 4,773,953 issued Sep. 27, 1988, is directed to a method for utilizing a personal computer, a video camera or the like to create graphics, images, or creative designs on a fabric.
U.S. Pat. No. 5,620,548 is directed to a silver halide photographic transfer element and to a method for transferring an image from the transfer element to a receptor surface. Provisional application 60/029,917 discloses that the silver halide light sensitive grains be dispersed within a carrier that functions as a transfer layer, and does not have a separate transfer layer. Provisional application 60/056,446 discloses that the silver halide transfer element has a separate transfer layer. Provisional Application 60/065,806 relates to a transfer element using CYCOLOR technology, and has a separate transfer layer. Provisional Application 60/065,804 relates to a transfer element using thermo-autochrome technology, and has a separate transfer layer. Provisional application 60/030,933 relates to a transfer element using CYCOLOR and thermo-autochrome technology, but having no separate transfer layer.
U.S. Pat. No. 5,798,179 is directed to a printable heat transfer material using a thermoplastic polymer such as a hard acrylic polymer or polylvinyl acetate) as a barrier layer, and has a separate film-forming binder layer.
U.S. Pat. No. 5,271,990 relates to an image-receptive heat transfer paper which includes an image-receptive melt-transfer film layer comprising a thermoplastic polymer overlaying the top surface of a base sheet.
U.S. Pat. No. 5,502,902 relates to a printable material comprising a thermoplastic polymer and a film-forming binder.
U.S. Pat. No. 5,614,345 relates to a paper for thermal image transfer to flat porous surfaces, which contains an ethylene copolymer or a ethylene copolymer mixture and a dye-receiving layer.
Provisional application 60/127,625, filed Apr. 1, 1999 relates to relates to a polymeric composition comprising an acrylic dispersion, an elastomeric emulsion, a plasticizer, and a water repellant.
One problem with many known transfer sheets is the loss of “hand” or the formation of hard or brittle images on the substrate. Over time, these image layers crack, chip and peel from the substrate resulting in a reduction in the esthetic appeal of the transfer image. For example, images prepared by conventional screen printing followed by dry heat transfer to a cloth substrate frequently crack and peel from the substrate with repeated laundering.
Additionally, polymer layers used to prepare laminate transfer sheets are frequently transferred to the substrate itself during dry heat transfer. The transferred polymeric materials also reduce the “hand” of the image printed substrate and often produce a halo of clear polymer around the transferred image. The transferred polymer halo detracts from the imaged substrate by reducing the sharpness and clarity of the transferred image.
The prior art has attempted to solve the polymer halo problem by applying an adhesive polymer or adhesive varnish over an image and in close register to the image. During heat transfer, the polymer or adhesive varnish covering the image bonds the image to the substrate only within the outline of the image thereby substantially eliminating the polymer halo. U.S. Pat. Nos. 3,959,555, 4,308,310 and 4,517,044 described different ways to achieve this result. Although these processes minimize the polymer halo, the transferred image remains susceptible to cracking and peeling. U.S. Pat. No. 4,786,349 describes a heat transfer process in which an absorbing sheet is used between a heated platen and a thermoplastic layer having characters printed thereon. The absorbing sheet has a greater affinity for softened or molten thermoplastic adhesive of the thermoplastic sheet and absorbs the heated adhesive, thereby minimizing the polymer halo transferred to the substrate. This method also, however, does not prevent the transferred image from cracking and peeling.
In an attempt to solve the halo problem, U.S. Pat. No. 5,741,387 provided for a laminated image transfer sheet having a support sheet, a heat release layer on the support sheet, an ink design layer on the heat release layer, a polymer containing a water-dispersible polymer on the ink design layer and a lacquer mask layer on the water-dispersible polymer layer. In particular, the mask layer was deposited on the water-dispersible polymer layer such that the mask layer outlined the ink design in the ink design layer, but did not cover the ink design itself. This allowed for transfer of only the heat release layer, the ink design and the water-dispersible polymer layer within the outlined ink design. However, there were several drawbacks to the process of U.S. Pat. No. 5,741,387. First, the problem of cracking, chipping and peeling of the image layers over time still existed. Second, the application of the image layer to the substrate required a considerable amount of pressure. Specifically, a pneumatic heat transfer press which exerts from 30 to 120 pounds per square inch (psi) was required. Thus, a conventional iron was rot sufficient for achieving the pressure necessary to transfer the image from the transfer sheet of U.S. Pat. No. 5,741,387 to a substrate, such as a tee shirt.
Accordingly, there continue to exist problems associated with clearly transferring an image to a substrate and providing for the “hand” or feel of the substrate after the image has been transferred. This need is also combined with the requirement that the transfer can be effected with the use of a conventional hand-iron.